Observation of a Vector Charmoniumlike State at $4.7\text{}\text{}\mathrm{GeV}/{c}^{2}$ and Search for ${Z}_{cs}$ in ${e}^{+}{e}^{-}\to {K}^{+}{K}^{-}J/\psi $

Using data samples with an integrated luminosity of $5.85\text{}\text{}{\mathrm{fb}}^{-1}$ collected at center-of-mass energies from 4.61 to 4.95 GeV with the BESIII detector operating at the BEPCII storage ring, we measure the cross section for the process ${e}^{+}{e}^{-}\to {K}^{+}{K}^{-}J/\psi $. A new resonance with a mass of $M=470{8}_{-15}^{+17}±21\text{}\text{}\mathrm{MeV}/{c}^{2}$ and a width of $\Gamma =12{6}_{-23}^{+27}±30\text{}\text{}\mathrm{MeV}$ is observed in the energy-dependent line shape of the ${e}^{+}{e}^{-}\to {K}^{+}{K}^{-}J/\psi $ cross section with a significance over $5\sigma $. The ${K}^{+}J/\psi $ system is also investigated to search for charged charmoniumlike states, but no significant ${Z}_{cs}^{+}$ states are observed. Upper limits on the Born cross sections for ${e}^{+}{e}^{-}\to {K}^{-}{Z}_{cs}\left(3985{\right)}^{+}/{K}^{-}{Z}_{cs}\left(4000{\right)}^{+}+c.c.$ with ${Z}_{cs}\left(3985{\right)}^{±}/{Z}_{cs}\left(4000{\right)}^{±}\to {K}^{±}J/\psi $ are reported at 90% confidence levels. The ratio of branching fractions $\left\{\left[B\left({Z}_{cs}\left(3985{\right)}^{+}\to {K}^{+}J/\psi \right)\right]/B\left[{Z}_{cs}\left(3985{\right)}^{+}\to \left({\overline{D}}^{0}{D}_{s}^{*+}+{\overline{D}}^{*0}{D}_{s}^{+}\right)\right]\right\}$ is measured to be less than 0.03 at 90% confidence level.